It's quite possible a re-install from disc will not be the same as what is currently installed, adding a Service Pack makes a newer version of the OS. It may be necessary to do a clean install then install SP3 afterward. Also involved is most of the OEMs/Brands use a Master HDD in a duplicating machine to produce cloned HDDs for each model of their computer and Windows is pre-activated in accordance with their licensing from Microsoft. The Product Key in that installation nearly always is different from the COA sticker on the computer and will be embedded in the factory restore disc or files on the restore partition.